DEVELOPMENT  OF  BRISTOL  GLAZE  BY 
USE  OF  PHOSPHATES 

BY 

RUSSELL  ELLSWORTH  ARNOLD 


THESIS 

FOR  THE 

DEGREE  OF  BACHELOR  OF  SCIENCE 

IN 

CERAMIC  ENGINEERING 


COLLEGE  OF  ENGINEERING 
UNIVERSITY  OF  ILLINOIS 


1922 


Digitized  by  the  Internet  Archive 
in  2015 


https://archive.org/details/developmentofbriOOarno 


TABLE  OF  CONTENTS. 


Page 

I.  Introduction:  1. 

(a) .  History. 

(b) .  Purpose  of  Investigation. 

(c) .  Survey  and  Discussion  of  Bristol  Glazes. 

II.  Procedure  and  Survey  of  this  Investigation;  3. 

(a) .  Type  Formula  Used. 

(b) .  Materials  Used  and  Layout  of  Series. 

(c) .  Preparation  of  Glazes  and  Methods  of  Blending. 

(d) .  Preparation  of  Body  Used. 

(e) .  Firing  of  Ware. 


III. 

Ceramic  Formulas  and  Batch  Weights: 

5. 

IV. 

(a) .  Formulas  of  Series. 

(b) .  Variations  of  Constituents. 

(c) .  Batch  Weights. 

(d)  . Example  of  Blending  Calculations. 

Series  I Aluminum  Phosphates: 

8. 

V. 

(a) .  Specific  Gravity  of  Glazes. 

(b) .  Oxygen  and  Alumina-Silica  Ratios. 
( C ) . Dipping  Properties  of  Glazes. 

(d).  Burning  Results. 

Series  II Calcium  Phosphates: 

10. 

VI. 

(a).  Specific  Gravity  of  Glazes. 

(bj.  Oxygen  and  Alumina-Silica  Ratios. 

(c) .  Dipping  Properties  of  Glazes. 

(d) .  Burning  Results. 

Series  III Barium  Phosphates: 

13. 

VII. 

(a) .  Specific  Gravity  Of  Glazes. 

(b) .  Oxygen  and  Alumina-Silica  Ratios. 

(c) .  Dipping  Properties  of  Glazes. 

(d) .  Burning  Results. 

Discussion:  of  Results: 

14. 

VIII. 

Conclusions : 

16. 

IX. 

Bibliography: 

17 

X. 

Acknowledgment : 

30. 

. 


%HE  DEVELOPMENT  OF  BRISTOL  GLAZE  BY 

USE  OF  PHOSPHATES. 

****** 


1. 


INTRODUCTION. 

The  term  Bristol  glaze  seems  to  have  oome  from  the  town 
in  England  called  Bristol.  From  all  reports  this  seems  to  be  the 
origin  of  the  name  of  what  is  now  called  the  Bristol  glaze  of  to- 
day. This  type  of  glazes  is  well  adapted  for  use  on  stoneware, 
terra  cotta,  brick,  and  porcelain  bodies.  Up  to  1885,  all  stone- 
ware seems  to  have  been  glazed  with  sodium  chloride  and  Albany 
slip.  The  use  of  a lead  glaze  for  such  ware  was  limited  and  due 
to  the  effeots  of  the  lead  on  the  glaze  workers  the  lead  content 
in  the  various  stoneware  glazes  was  eliminated  gradually  and  sub- 
stituted with  zinc  oxide.  At  last,  all  lead  was  removed  and  a 
white  opaque  glaze  resulted.  In  1884  the  Bristol  glaze  was  ex- 
hibited at  New  Orleans,  and  from  all  reports  this  was  the  first 
appearance  of  the  Bristol  glaze  in  this  country.  Some  author- 
ities differ  as  to  whether  the  glaze  was  first  used  in  America  or 
England.  However,  about  1884  seems  to  mark  the  beginning  of  the 
use  of  such  a glaze  in  this  country.  The  earlier  forms  were  ap- 
plied by  rolling  the  ware  in  clay  and  flint.  The  ware  was  burned 
and  the  customary  salt  glaze  applied.  This  method  gave  a glaze 
very  much  like  the  present  day  Bristol,  both  in  appearance  and 
composition.  (1). 


From  notes  on  lecture  on  "Glazes"  by  Prof.  C.  W.  Parmelee,  Uni- 
versity of  Illinois.  (1). 


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2. 

Since  the  year  of  1384,  the  Bristol  glaze  has  developed 
until  now  it  plays  an  important  part  in  the  stoneware  industry. 
Variations  have  been  made,  but,  in  the  main,  the  glaze  is  composed 
of  three  fluxes:  potassium  oxide,  calcium  oxide,  and  zinc  oxide; 
the  intermadiate,  alumina;  and  the  acid  constituent,  flint.  (1). 

Up  to  the  present  date,  there  has  been  little  or  no  work  i 
done  on  the  effect  of  phosphates  on  a Bristol  glaze.  There  have 
been  several  ideas  carried  out  regarding  the  addition  of  small 
portions  of  bone  ash,  and  one  investigation  by  Prof.  C.  W.  Parmelee 
on  the  effects  of  aluminum  phosphate  on  glaze  behavior.  (2).  It 
was  due  to  the  suggestion  of  Prof.  C.  W.  Parmelee,  that  this  in- 
vestigation was  undertaken,  and  the  author  wishes  to  thank  him 
for  the  aid  and  support  rendered  during  the  experiment ing. 

It  was  the  purpose  of  this  investigation  to  see  what 
effect  various  phosphates  had  on  the  development  of  a Bristol 
glaze;  to  study  carefully  their  behavior  and  at  the  same  time 
find  out  what  would  be  the  best  glaze  compositions. 

The  glaze  develops  and  matures  around  cone  5 and  cone 
8,  is  generally  used  on  stoneware  and  terra  cotta,  and  in  some  in- 
stances, brick  and  porcelain  bodies.  Due  to  the  nature  of  the 
glaze,  it  can  be  used  on  ware  either  bone  dry  or  leather,  and 
can  be  burned  in  unwadded  saggers. 


(1) .  Notes  on  lecture  on  "Glazes”  by  Prof.  C.  w.  Parmelee. 

(2) .  Transactions  American  Ceramic  Society,  Volume  8,  Page  237. 


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3. 


II.  PROCEDURE  AND  SURVEY  OF  WORK. 

The  type  formula  used  was  one  which  develops  at  about 
cone  6,  (1350°  G)  ,in  from  36  to  40  hours.  The  ceramic  formula 
for  this  glaze  is  as  follows; 

. 333  K20  ) ( 

.333  CaO  ) . 55  A1 20  3 ( 3.3  S iO  2 . 

, 333  ZnO  ) ( 

Three  phosphates:  aluminum,  calcium,  and  barium,  were  used  as  the 
main  variables,  with  zinc  phosphate  used  occasionally  to  fill  in 
and  give  the  required  P20g  content.  This  investigation  consisted 
mainly  of  three  series,  namely:  Series  I,  made  up  by  the  use  of 

aluminum  phosphate  giving  as  variables  P20s  and  AI2O3;  Series  II, 
made  up  by  the  use  of  calcium  phosphate,  giving  as  variables  P2O5, 
CaO, and  ZnO,  the  latter  varying  together;  and  Series  III,  made  up 
by  the  use  of  barium  phosphate,  giving  as  variables  P2O5,  and  BaO, 
and  ZnO,  the  latter  varying  together. 


The  materials  used  were: 


Potassium  Carbonate  (K2CO3)  source 

giving 

k20. 

Calcium  Carbonate 

(CaCOg)  source 

giving 

CaO 

Calcium  Phosphate 

Ca3(P04)2  source 

s giving 

CaO  and  P205 

Zinc  Oxide  (ZnO) 

source 

giving 

ZnO 

Zinc  Phosphate 

Zn3(P0^)2  source 

giving 

ZnO  and  P205 

H.  & G.  A-l  English  China  Clay 

giving 

Al203and  Si02 

Flint 

giving 

Si02 

Barium  Carbonate 

(BaC03)  source 

giving 

BaO 

Barium  Phosphate 

Ba3(P0^)2  source 

i giving 

BaO  and  P20g 

. 


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. 

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arts3 


4. 


The  batches  were  mixed  and  ground  wet  from  4 to  5 hours 
in  glaze  pebble  mills.  They  were  then  lawned  through  120  mesh 
and  the  specific  gravity  adjusted  to  about  24  ounces  to  the  pint. 

The  variable  glaze  compositions  were  made  up  by  blend- 
ing the  extremes  to  get  the  intermediates.  The  blending  was  done 
by  weight  on  the  batch  weight,  basis.  The  glazes  were  then  dipped 
on  Bloomingdale  stoneware  trial  pieces,  and  prepared  for  burning. 

The  trial  pieces  were  made  up  of  the  above  mentioned 
clay  prepared  by  pugging  in  a wet  pan  and  running  the  plastic 
clay  through  an  auger  machine.  The  trial  pieces  were  cut  and 
dried  in  a steam  dryer  until  they  were  "bone  dry". 

The  firing  was  done  in  coal-fired,  down-draft  test 
kilns,  burning  bituminous  coal  of  a fairly  good  grade.  The  ware 
was  set  in  unwadded  saggers,  and  burned  at  three  cones:  namely, 

3,  6,  and  10,  and  burned  for  40  hours. 


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5 


III.  CERAMIC  FORMULAS  AND  WEIGHTS. 


In  order  to  use  phosphates  only  to  give  the  PgO^  content 
there  are  certain  limits  within  which  the  formulas  had  to  stay. 

The  ceramic  formulas  with  the  variables  for  each  series  are  as 
follows : 

Series  I. 


.333 

.333 

.333 

k2o 

CaO 

ZnO 

! 

.3  - .6  A1 

pO  ( 3.3  S iO  p 

5 ( .05-. 3 P205 

Series 

II. 

.300 

.14-. 42 
.56-. 38 

KpO 

cao 

ZnO 

S 

.55  AlgOj 

i 3.3  S10„ 

( -07-21  pA 

Series 

III. 

.300 
.0  - .4 
.4  - .0 

k2o 

BaO 

CaO 

) 

.55  AlgOj 

j 3.3  SiOp 

( . It*.  2 P205 

Series 

I. 

Diagram  of  Field  df  Series  I. 


1 2 3 4 5 6 7 


Moles  . 3 

of 

.18 

P2°5 

.05 

c 

B 

A 

.3  .35  .40  .45  .50  .55  ..60 

Moles  of  A1_0„ 

2 3 


* 


. 


. 


6 


The  batch  weights  of  the  extremes  of  the  first  series 
are  given  as  follows: 


A-l. 


A-6. 


C-l. 


C-6. 


K2CO3. 
CaC03. 
ZnO. . . 

aipo4. 

Clay. . 


46.0 

33.3 

37.0 

13.3 
64.5 


Flint.  .168.0 


K3CO3.  . 46.0 
CaCOj. . 33. 3 

ZnO 37.0 

A1P0  . . 13.3 
Clay? . . 143.0 
Flint. .132.0 


KPC0,..  46.0 
33.3 


CaC03  > 
ZnO. . . . 


37.0 


A1PQ  . . . 73. 3 

Clay. . . 

Flint. .198.0 


KpCO.?.  . 

CaCof . . 
ZnO.r. . 
A1P0  . . 
Clay. . . 


46.0 

33.3 

27.0 
73.2 

77.4 
Flint. .103.0 


Series  II. 


Diagram  of  Field  Of  Series  II. 

13  3 4 

Moles  .3 
of 

P 0 
3 5 


.3 


.1 


B 


.3  .3  .4  .5 

.8  .7  .6  .5 

Moles  of  CaO  and  ZnO 


A. 

.6  CaO 
.4  ZnO 


A-l. 

KpCO 59.5 

ZnO 26.5 

Ca3 (PO/ ) p« • 18. 3 
Zni(P0A)p. .13.1 
Clly.  .7.7.202.5 
Flint 188.0 


A-5. 

KpCO, 59.5 

ZnO.? 32.4 

Caa(P04)2.37.8 
Ca0O-.T.  7.  30.0 
Clay. . . . . 202.  5 
Flint. . . . 188.0 


C-l. 


K0CQ3 59.  5 

ZnO: 8.1 

Ca, ( P^A ) p • 18 • 3 
ZnS(P0;) p.89.5 
Clay.  .7.7203.5 
Flint. . . . 188.0 


C-5. 

KpCO, 59.5 

ZflO.r 8.1 

Ca3 ( P0A) p. 55. 6 
Zn, (P04) p. 38. 5 
Clay. .7. 7202. 5 
Flint 188.0 


Series  III. 


Diagram  of  Field  of  Series  III. 


Moles  . 2 
of 

P3°5 

.1 


.4 

.0 


.3 

.1 


.2 

.2 


.1 

.3 


B 


.0  ZnO 
. 4 BaO 


Moles  of  ZnO  and  BaO 


7 


A-l. 


A-5. 


B-l. 


B-5. 


Z2C03 41.4 

ZnO ..«•»«• 34 • 3 


C3in  ( P04  ) p.  31 . 0 
CaC03. 7.7.10.0 
Clay 142.0 


FI  int  • • • .132.0 


^■3^3*  * * • ^ 

ZnO ......  24 . 3 

Ba3(P04)?60.1 

BaCO^.T. 719.7 

Clayr. . .142.0 

Flint. . .132.0 


K2C03 41.4 

Zn3 (po4) B 
Ca3(P04)o31.0 
CaC03. . . ,10.0 
Flint. . .132.0 
Clay: . . . 143.0 


KqC03« . , .41.4 
Zn3 ( PO4 ) 338. 5 
Ba3(P04)260.1 
BaCO,. 7.719.7 
Flint. . .143.0 
Clay. . . .142.0 


In  calculating  the  glaze  compositions  and  blending 

to  get  the  intermediates,  the  batch  weight  method  was  used.  As 

an  example,  say  there  are  four  glazes,  each  varying  in  composition 

as  in  the  above  glazes.  The  intermediates  are  obtained  by, 

first  mixing  up  the  extremes,  and  then  dividing  the  extremes 

up  into  parts  as  follows; 

A . B . C • D 

100$  A.  66$  A.  33$  A.  0$  A. 

0$  D.  34$  D.  66$  D.  100$  D. 

The  100$  of  A for  instance  is  taken  as  100$  of  the  batch  weight. 


8. 


IV.  SERIES  I.-  ALUMINUM  PHOSPHATE- 

The  formula  and  method  of  procedure  was  given  above, 
hence  this  division  and  the  two  divisions  following  give  the  re- 
sults obtained  in  both  dipping  and  burning  the  glazes. 

The  oxygen  ratio  of  these  glazes  range  from  2.9  - 4.0. 
The  Al^Og-SiOg  ratio  range  from  l/5.5  to  l/6. 

The  glaze  extremes  were  weighed  and  found  to  be  as 

follows : 


A-l 23.2  ounces  per  pint. 

A-6 24.6  ounces  per  pint. 

C-l 24.2  ounces  per  pint. 

C-6 25.6  ounces  per  pint. 


When  these  glazes  were  blended  as  described  above  the 
specific  gravity  ranged  from  23.2  to  25.5.  This  was  about  the 
correct  consistency  for  dipping. 

As  a whole,  the  glazes  dipped  well,  except  in  a few 
cases  and  then  spraying  was  resorted  to  which  proved  a remedy. 

Results  of  Cone  3:  This  cone  temperature  was  not  suf- 

ficiently high.  The  glazes  in  general  were  immature  and  appeared 
to  be  merely  sintered.  There  are  a few  results  that  were  very 

obvious  that  may  be  well  to  mention.  With  a low  A1  0 content 

3 3 

glazes  were  immature.  With  increasing  P3O5  the  fusibility  seemed 
to  increase.  The  color  was  about  the  same  throughout  the  varia- 
tions, the  only  color  being  a white  with  a gradual  darkening  as 
P3O5  and  Al^Oj  increase.  As  a whole  the  glazes  were  poorly  de- 
veloped giving  none  that  was  good. 


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r;  rn^  . 


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9. 

Results  of  cone  6:  The  results  of  this  temperature  were 

very  similar  to  the  cone  3 burn.  The  increase  in  heat  treatment 
showed  little  change  in  the  maturity  of  the  glazes.  With  an  in- 
crease in  P3O5  content  the  fusibility  increased  which  leads  to  the 
conclusion  that  this  is  true  in  general.  There  was  no  apparent 
effect  upon  the  color,  because  the  RO  group  content  remained  con- 
stant, and  upon  this  group  depends  the  constituents  for  giving  the 
color.  The  results  of  this  temperature  show  no  signs  of  any 
glaze  possibilities  at  this  cone. 

Results  of  cone  10:  The  results  of  this  burn  were  a 

little  more  satisfactory  than  the  lower  cones.  The  trial  pieces 
did  not  withstand  this  temperature  and  were  consequently  over- 
burned. This  only  made  it  a little  more  difficult  to  judge  the 

glazes.  The  glazes  of  low  AI2O3  content  showed  no  signs  of 

maturity  as  in  the  above  cases,  but  as  the  AI2O3  content  increased 
an  increasing  maturity  resulted  until  the  glazes  were  of  a glossy 
texture.  Glazes  A-4,  B-4,  C-4,  A-5,  and  above  were  the  best  ones. 
Of  these,  glaze  A-4  proved  the  best.  At  this  temperature  the 
glazes  appeared  transparent  with  the  gray  color  of  the  body  im- 
parted to  the  glaze.  In  general,  this  series  required  about 
cone  10  the  develop  the  glaze. 


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10. 


V.  SERIES  IX.  - CALCIUM  PHOSPHATE. 

The  oxygen  ratio  of  this  series  range  from  2.6  to  2,9. 

The  Al„0„-Si0_  ratio  was  constant  at  l/6. 

a O a 

The  glazes  of  this  series  dipped  with  better  results  than 
Series  II.  In  fact  the  dipping  properties  were  good.  The  speci- 
fic gravity  of  these  glazes  was  about  25  ounces  per  pint. 

Results  of  cone  3:  The  glazes  of  this  series  were  not 

matured  as  in  Series  I and  cone  3 burn.  The  same  results  were 
apparent  regarding  the  increasing  P3O5  content.  The  glazes  at 
this  temperature  crawled  a little..  This,  perhaps,  was  due  to  the 
high  raw  clay  content.  To  remedy  this  the  raw  clay  should  be 
calcined  and  should  not  be  added  much  above  .2  equivalents.  The 
color  of  these  glazes  was  white.  This  was  due  to  the  zinc  oxide 
content  in  the  glaze.  In  general  there  were  no  glazes  that 
turned  out  well. 

Results  of  cone  6:  There  were  no  good  glazes  developed, 

but  the  glazes  showed  more  signs  of  maturity. 

Results  of  cone  10:  The  results  of  this  burn  were  the 

best  in  comparison  to  the  other  cone  temperatures.  The  de- 
creasing ZnO  and  increasing  CaO  glazes  became  more  transparent 
which  may  be  due  entirely  to  the  decrease  in  ZnO  content.  The 
increased  fusibility  due  to  increased  PgOg  content  was  again 
evident.  All  glazes  except  A-l,  A-2,  A-3,  and  A-4  were  good. 

They  developed  a good  glossy  texture,  but  were  transparent  giv- 
ing the  grayish  color  of  the  body.  The  glazes  showed  no  signs 


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11. 

of  crazing  or  crawling.  The  gloss  developed  at  this  tempera- 
ture was  good,  and  especially  this  was  true  with  glaze  A-4. 


. 


12. 


V.  SERIES  III.  - BARIUM  PHOSPHATE. 

The  oxygen  ratio  lies  within  the  range  of  2.7  to  2.9, 
while  the  A^Qg-SiOg  ratio  remained  the  same  value  of  1/6. 

The  specific  gravity  for  this  series  was  made  to  be  about 
24.0  to  25.0  ounces  per  pint.  This  series  resembled  Series  II 
in  dipping  properties.  The  trial  pieces  dipped  well  giving  a 
good  smooth  finish. 

Results  of  cone  3:  This  series  developed  the  best 

glazes  of  all  three  series.  Glazes  B-3,  B-4,  and  B-4  were  matured 

with  a fair  glossy  texture.  Of  all  these,  glaze  B-4  was  the  best. 

This  glaze  is,  perhaps, the  only  satisfactory  one  at  this  cone  while 
at  a higher  cone  much  better  glazes  developed.  The  color  of  these 
glazes  was  a grayish  white. 

Re suit g of  cone  6:  As  might  be  expected  the  increased 

heat  treatment  given  the  poor  glazes  greatly  Improved  the  nature 
of  the  glazes  above  those  of  cone  3.  Still  the  glazes  of  low 

P205  content  showed  signs  of  immaturity,  but  glazes  B-l,  B-2,  B-3, 
B-4,  and  B-5  were  all  developed  with  a good  glossy  texture.  Of 

all  these  glazes  B-3  was  the  best.  The  others  showed  signs  of 
crawling  slightly.  Glaze  B-3  gave  a good  gloss,  and  was  gray  in 
color.  The  amount  of  crawling  mentioned  above  can  be  remedied 
easily  and  will  give  several  good  glazes. 

Results  of  cone  10:  The  results  of  this  burn  were  good. 

Glazes  were  matured  giving  a fair  glossy  texture.  There  was  no 


crazing,  crawling,  and  the  glaze  was  transparent  with  the  gray  of 


. 


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the  body  showing  through.  All  the  glazes  developed  alike  show- 
ing little  variation.  This  burn  resulted  in  some  good  glazes, 
but  the  best  were  the  ones  of  about  a one  to  one  ratio  of  CaO  and 
ZnO. 


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14 


VII.  DISCUSSION  OF  RESULTS. 


A comparison  of  the  oxygen  and  alumina-silica  ratio  is 
desirable.  • As  given  by  several  authorities,  the  oxygen  ratio 
for  a Bristol  glaze  should  be  from  2.3  to  2.5.  The  alumina-silica 
ratio  is  usually  around  l/6  to  l/7.  The  glazes  falling  under  these 
classifications  are  supposed  to  mature  satisfactorily.  It  is 
possible,  however,  to  lower  the  alumina-silica  ratio  with  a low 
alumina  content  and  run  into  the  field  of  good  matt  glazes. 

Under  Series  I,  the  oxygen  ratio  ranges  from  2.9  to  6.0. 
According  to  the  results  it  was  very  evident  that  glazes  with 
oxygen  ratio  above  2.7  were  not  developed.  One  might  conclude, 
then,  that  the  composition  was  impossible  as  a glaze  and  would 
not  develop  under  any  consideration.  The  alumina-silica  ratio 
given  for  a Bristol  glazeis  usually  l/6  to  l/7.  This  comparison 
shows  that  ratio  given  above  for  these  glazes  is  about  normal. 

Under  Series  II.  the  oxygen  ratio  was  2.6  to  2.9  and 
the  alumina-silica  ratio  was  l/6.  Both  of  these  ratios  prove 
satisfactory  according  to  the  requirements  and  in  comparison  with 
the  results,  this  is  true  because  the  glazes  developed  far  better 
in  this  series  than  in  Series  I. 

The  ratios  for  Series  III  are  3.7  to  3.9  for  the  oxygen 
ratio  and  i/6  for  the  alumina-silica  ratio.  The  same  is  true  of 
Series  III  as  is  true  of  Series  lx  in  regard  to  the  correct  ratios 
for  the  glazes  compositions.  However,  Series  III  glazes  developed 
much  better  than  Series  I.  In  general  that  best  glazes  fell  with- 


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15. 


In  the  limits  of  the  oxygen  and  alumina-silica  ratios  of  typical 
Bristol  glazes. 

It  might  be  well  to  discuss  the  body  usedmin  this  inves- 
tigation. The  Bloomingdale  stoneware  body  used  worked  nicely  at 
cone  3 and  cone  6,  but  when  cone  10  was  reached  the  body  showed 
signs  of  overburning.  It  is  possible  to  develop  these  glazes  on 
porous  tile  trial  pieces,  which  would  prove  better  at  the  higher 
temperature.  Due  to  this  overburning,  it  was  rather  hard  to 
judge  the  glazes  to  any  advantage  at  cone  10. 

There  was  a great  deal  of  flaking  and  cracking  of  some 
of  the  glazes.  This  was  not  true  of  all,  but  those  glazes  that 
were  bad  were  not  improved  when  sprayed.  The  author  is  of  the 
opinion  that  a substitution  of  ball  clay  and  calcined  kaolin  for 
some  of  the  raw  clay  would  give  the  glazes  better  dipping  proper- 
ties. From  all  indications  the  dipping  properties  had  little 
effect  in  the  development  of  the  phosphate  Bristol  glazes,  but  such 
remedies  would  prove  beneficial  for  some  of  the  glazes. 

A fusion  test  was  run  on  the  extremes  of  the  various 
series  and  not  much  could  be  learned  from  the  results.  The  glazes 
were  made  up  in  cones  and  placed  along  side  of  standard  cones. 

The  results  showed  that  the  glazes  went  down  at  cone  3 to  cone  4. 


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16 


VIII.  CONCLUSIONS* 

In  concluding  there  are  several  general  results  which 
may  be  stated.  These  follow  time  after  time  and  are  facts  pro- 
ven. They  will  be  given  at  the  end  of  this  section*  There 
are  several  difficulties  arising  when  developing  a Bristol  glaze 
by  the  use  of  phosphates.  This  invest igation  does  not  complete 
the  work  that  is  at  all  possible,  but  it  reveals  several  diffi- 
culties that  should  be  overcome  should  such  an  investigation  be 
tried  further.  The  author  is  of  the  opinion  that  by  reducing 
the  alumina-silica  content,  still  keeping  the  proper  ratio,  i.  e. , 
l/6  to  l/7,  the  flux  content  would  be  increased  in  proportion  and 
this  would  make  a less  refractory  glaze.  What  is  desired  is  a 
glaze  which  develops  at  about  cone  6.  The  Bloomingdale  stoneware 
will  not  stand  a higher  temperature  with  good  results.  It  is 
also  suggested  that  biscuit  trial  pieces  be  used.  This  will 
allow  a higher  temperature  to  be  used  to  develop  the  glazes. 

In  Series  II  there  appeared  a solution  of  the  ZnO  with 
increasing  P^Og  content  giving  transparency. 

Through  all  series  an  increase  in  P3O5  content  caused 
fusibility  to  increase. 

ZnO  and  BaO  developed  better  glazes  than  ZnO  and  CaO 
and  were  best  at  equal  parts  of  ZnO  and  BaO. 

With  an  increase  in  PgOg  oontent  the  ZnO  was  taken  up 
in  solution  more,  resulting  in  a more  transparent  glaze. 


17 


XI,  BIBLIOGRAPHY. 

There  is  not  much  literature  on  this  subject,  but  what 
was  at  all  available,  the  author  went  over  and  picked  out  the 
most  important  parts. 

In  Chemical  Abstracts,  1909,  5:3885,  K.  Huthrer  says, 
"When  extremely  finely  pulverized  SiOg  is  heated  with  an  excess 
of  H3PO4  in  a quartz  tube,  a clear  solution  results,  first.  On 
further  heating,  a white  pulverent  precipitate  separates  which 
appears  under  the  microscope  as  a mixture  of  fine  rods,  hexagonal 
plates  and  octahedra.  Analysis  shows  that  it  has  the  composition 
SiOg.PgOg,  and  the  name  Silioyl  Phosphate  has  been  chosen.  The 
compound  may  be  prepared  also  by  heating  for  a long  time  in  a 
platinum  dish,  a mixture  of  SiCl^  and  H3PO4.  At  ordinary  temp- 
eratures it  is  fairly  stable  and  decomposes  only  before  the  oxy- 
hydrogen  flame.  At  moderate  temperatures  P^O^  is  slowly  driven 
off  and  the  crystalline  form  disappears.  Heated  in  a current  of 
steam  a steady  loss  in  weight  occurs.  It  resists  the  attack  of 
strong  acids  except  HF,  but  is  decomposed  by  NaOH  and  NagCC^.  Just 
as  SiO^  is  attack  by  H3PQ4,  so  also  is  glass.  The  results  of  a 
number  of  experiments  may  be  summed  up  in  the  statement  that  in 
the  latter  case  the  following  compounds  may  be  produced:  SiP20j, 
NaP03  or  KP03,  Ca3(P04)2  and  AIPO3. " 


In  Chemical  Abstracts,  Volume  10,  2036,  C.  H.  Kerr  says: 
"Bone  ash  should  be  used  with  KN03  and  As^Qjj  to  increase  fluidity. 
Adding  a small  amount  of  Pb304  makes  a softer  and  more  brilliant 


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18. 


glass,  especially  good  for  taking  colors.  Some  borax  should  also 
be  used". 

In  Chemical  Abstracts,  volume  11,  2709,  C.  G.  Memminger 
says:  "Natural  phosphates  containing  SiOgand  CaCQ^  are  calcined 

at  1400-1500°  C.  to  drive  off  volatile  matter  and  decompose  the 
CaCOj,  yielding  CaO  which  combines  with  SiOs.  The  Ca3(P04)2  is 
not  affected. n 

In  Chemical  Abstracts,  volume  13,  1002,  H.  Fritz  says: 
"Glasses  and  glazes  were  prepared  from  mixtures  of  PbO,  alkalies, 
lime,  BaO,  or  ZnO,  and  P2O5  or  a phosphate.  When  a phosphate  was 
used  the  products  were  not  clear,  but  when  P3O5  was  used,  they 
were  mostly  clear  and  occasionally  brilliant.  In  some  cases  the 
introduction  of  .15  equivalents  of  AlgO^  made  a turbid  glass  or 
glaze  become  more  clear.  Most  of  the  glazes  prepared  with  PgOg 
were  subject  to  crazing.  Brilliant  glazes  free  from  crazing  were 
obtained,  however,  with  a mixture  of  the  compounds.  (0.1  K2O,  0.1 
CaO,  0.8  PbO,  0.3  AI3O3,  and  3.0  P30g.  " 

In  the  Transactions  of  the  American  Ceramic  Society, 
volume  7,  page  205,  Binns  says:  "Calcium  phosphate  is  practically 
infusible,  and  there  is  no  doubt  that  its  function  in  a body  is 
to  uphold  the  mixture  and  to  enable  it  to  endure  a more  severe 
fire  than  it  otherwise  would. " The  same  volume  on  page  374,  he 
states  that  the  effect  of  bone  ash  in  ceramic  mixtures  is  highest 
in  fusibility  at  17$.  The  physical  structure  of  the  bone  has  no 
effect.  The  infusibile  character  of  the  bone  china  depends  upon 
an  excess  of  bone. 


. 


4 


< » 


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19. 


In  Transactions  of  the  American  Ceramic  Society,  volume 
10,  page  341,  Stull  says:  "The  use  of  bone  ash  is  a direct  cause 

of  flaking  of  the  glaze.  Flaking  is  overcome  by  calcining  the 
bone  ash  with  flint.  Replacement  of  CaO  from  whiting  by  CaO  from 
bone  ash  increases  refractoriness  materially  and  induces  crazing." 
In  volume  10  page  343,  he  also  says:  " Bone  ash  is  used  as  an  opac- 
lfier  in  glazes;  excess  of  opacifier  causes  beading. " 

In  the  Transactions,  volume  8,  page  337:  Prof.  C.  W. 
Parmelee  says:  "Presence  of  phosphoric  acid  gives  translucency  if 
in  sufficient  amounts  and  tends  toward  improvement  in  color;  acts 
as  a flux  and  vitrifying  agent.  With  a slight  increase  of  SiOg, 
fusibility  is  increased.  Presence  of  0.3  equivalents  of  potash 
does  not  effect  translucency,  but  increases  fusibility  and  causes 
the  enamel-like  appearance."  This  was  on  a body  composition. 


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X.  ACKNOWLEDGMENT. 


Parmelee, 
wishes  to 
tione. 


It  was  due  to  the  aid  and  support  of  Prof.  C.  W. 
that  this  investigation  was  carried  on  and  the  author 
take  this  means  of  expressing  thanks  for  such  sugges- 


